Field of the Invention
The present invention relates to a novel process for preparing 3,5-bis(fluoroalkyl)pyrazole derivatives.
Description of Related Art
Polyfluoroalkylpyrazolylcarboxylic acid derivatives and 3,5-bis(fluoroalkyl)pyrazoles are valuable precursors for fungicidal active ingredients (for example WO 2003/070705, WO 2008/013925, WO 2012/025557).
Pyrazolecarboxylic acid derivatives are typically prepared by reacting acrylic acid derivatives having two leaving groups with hydrazines (e.g. WO 2009/112157 and WO 2009/106230). WO 2005/042468 discloses a process for preparing 2-dihaloacyl-3-aminoacrylic esters by reacting acid halides with dialkylaminoacrylic esters and subsequent cyclization thereof with alkyl hydrazines. WO 2008/022777 describes a process for preparing 3-dihalomethylpyrazole-4-carboxylic acid derivatives by reacting α,α-difluoroamines in the presence of Lewis acids with acrylic acid derivatives and subsequent reaction thereof with alkyl hydrazines.
3,5-Bis(fluoroalkyl)pyrazoles are prepared by reacting bisperfluoroalkyl diketones (e.g. 1,1,1,5,5,5-hexafluoroacetylacetone) with hydrazines (see Pashkevich et al., Zhurnal Vsesoyuznogo Khimicheskogo Obshchestva im. D. I. Mendeleeva (1981), 26(1), 105-7). The yield is only 27 to 40%. The synthesis, isolation and purification of the polyfluoroalkyl diketones is very complex since the compounds are generally very volatile and highly toxic.
In the light of the prior art described above, it is an object of the present invention to provide a process that does not have the aforementioned disadvantages and hence gives a route to 3,5-bis(fluoroalkyl)pyrazole derivatives in high yields.